HealthDay News -- Obesity increases a person's risk for a certain type of colorectal cancer, while exercise lowers the risk, according to a new study.

Researchers analyzed data from women in the U.S. Nurses' Health Study and men in the Health Professionals Study to determine if there was a link between weight, exercise and the risk for CTNNB1-positive or CTNNB1-negative colorectal cancer.

CTNNB1 is a molecule implicated in cancer and obesity.

A higher body-mass index, or BMI (a measurement of body fat based on height and weight), was associated with an increased risk of CTNNB1-negative colorectal cancer, while physical activity was associated with a lower risk.

BMI and physical activity had no effect on the risk for CTNNB1-positive colorectal cancer, according to the study appearing Feb. 26 in the journal Cancer Research .

"Our results provide additional evidence for a causal role of obesity and a physically inactive lifestyle in a specific molecular subtype of colorectal cancer," Dr. Shuji Ogino, an associate professor of pathology at Dana-Farber Cancer Institute and an associate professor in the department of epidemiology at Harvard School of Public Health, said in a journal news release.

"If physicians are able to identify individuals who are prone to develop CTNNB1-negative cancer, then it would be possible to strongly recommend physical activity," Ogino added.

The findings also suggest that CTNNB1 could be a potential target for drugs to prevent and treat colorectal cancer in certain patients, Ogino said.